Phage Therapy Pharmacology: Calculating Phage Dosing

Phage therapy, which can be described as a phage-mediated biocontrol of bacteria (or, simply, biocontrol), is the application of bacterial viruses-also bacteriophages or phages-to reduce densities of nuisance or pathogenic bacteria. Predictive calculations for phage therapy dosing should be useful toward rational development of therapeutic as well as biocontrol products. Here, I consider the theoretical basis of a number of concepts relevant to phage dosing for phage therapy including minimum inhibitory concentration (but also "inundation threshold"), minimum bactericidal concentration (but also "clearance threshold"), decimal reduction time (D value), time until bacterial eradication, threshold bacterial density necessary to support phage population growth ("proliferation threshold"), and bacterial density supporting half-maximal phage population growth rates (K-B). I also address the concepts of phage killing titers, multiplicity of infection, and phage peak densities. Though many of the presented ideas are not unique to this chapter, I nonetheless provide variations on derivations and resulting formulae, plus as appropriate discuss relative importance. The overriding goal is to present a variety of calculations that are useful toward phage therapy dosing so that they may be found in one location and presented in a manner that allows facile appreciation, comparison, and implementation. The importance of phage density as a key determinant of the phage potential to eradicate bacterial targets is stressed throughout the chapter.